Role of Stress-controlled Flow Pathways in HDR Geothermal Reservoirs

Ito, Takatoshi; Hayashi, Kazuo

doi:10.1007/pl00012563

Cited by 41 publications

(14 citation statements)

References 13 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…These observations are supported, for example, by work described in [5], where the concept is applied to geothermal reservoirs to detect flow pathways. Regarding the effect of redistributed stresses, a number of studies have been conducted about the permeability alterations around the excavated openings [6,7].…”

Section: Introductionmentioning

confidence: 74%

Stress-dependent permeability of fractured rock masses: a numerical study

Min

Rutqvist

Tsang

et al. 2004

International Journal of Rock Mechanics and Mining Sciences

454

233

View full text Add to dashboard Cite

We investigate the stress-dependent permeability issue in fractured rock masses considering the effects of nonlinear normal deformation and shear dilation of fractures using a two-dimensional distinct element method program, UDEC, based on a realistic discrete fracture network realization.A series of "numerical" experiments were conducted to calculate changes in the permeability of simulated fractured rock masses under various loading conditions. Numerical experiments were conducted in two ways: (1) increasing the overall stresses with a fixed ratio of horizontal to vertical stresses components; and (2) increasing the differential stresses (i.e., the difference between the horizontal and vertical stresses) while keeping the magnitude of vertical stress constant.These numerical experiments show that the permeability of fractured rocks decreases with increased stress magnitudes when the stress ratio is not large enough to cause shear dilation of fractures, whereas permeability increases with increased stress when the stress ratio is large enough.Permeability changes at low stress levels are more sensitive than at high stress levels due to the nonlinear fracture normal stress-displacement relation. Significant stress-induced channeling is observed as the shear dilation causes the concentration of fluid flow along connected shear fractures.Anisotropy of permeability emerges with the increase of differential stresses, and this anisotropy can become more prominent with the influence of shear dilation and localized flow paths. A set of empirical equations in closed-form, accounting for both normal closure and shear dilation of the fractures, is proposed to model the stress-dependent permeability. These equations prove to be in good agreement with the results obtained from our numerical experiments.2

show abstract

Section: Introductionmentioning

confidence: 74%

Stress-dependent permeability of fractured rock masses: a numerical study

Min

Rutqvist

Tsang

et al. 2004

International Journal of Rock Mechanics and Mining Sciences

454

233

View full text Add to dashboard Cite

show abstract

“…It follows that fluid flow through lowporosity hydrothermally altered geothermal and petroleum reservoir systems also favors preferential transport through macroscopic fractures. The hypotheses for why shear fractures that are critically stressed for slip are the most permeable include that they have been recently reactivated and, therefore, have the least amount of cement and precipitate (Ito & Hayashi 2003;Chaudhuri et al 2012), and that enhanced permeability is localized to the tips of critically stressed fractures, because of the associated strain heterogeneity (Tamagawa & Pollard 2008). Our experiments do not test these hypotheses, but indicate that fracture zones dilate as they approach frictional failure and may thereby increase in permeability even in the absence of these other effects.…”

Section: In Situ Fracture Permeabilitymentioning

confidence: 99%

Stress‐dependent transport properties of fractured arkosic sandstone

French

Chester

et al. 2016

Geofluids

View full text Add to dashboard Cite

We measure the fluid transport properties of microfractures and macrofractures in low-porosity polyphase sandstone and investigate the controls of in situ stress state on fluid flow conduits in fractured rock. For this study, the permeability and porosity of the Punchbowl Formation sandstone, a hydrothermally altered arkosic sandstone, were measured and mapped in stress space under intact, microfractured, and macrofractured deformation states. In contrast to crystalline and other sedimentary rocks, the distributed intragranular and grain-boundary microfracturing that precedes macroscopic fracture formation has little effect on the fluid transport properties. The permeability and porosity of microfractured and intact sandstone depend strongly on mean stress and are relatively insensitive to differential stress and proximity to the frictional sliding envelope. Porosity variations occur by elastic pore closure with intergranular sliding and pore collapse caused by microfracturing along weakly cemented grain contacts. The macroscopic fractured samples are best described as a two-component system consisting (i) a tabular fracture with a 0.5-mm-thick gouge zone bounded by 1 mm thick zones of concentrated transgranular and intragranular microfractures and (ii) damaged sandstone. Using bulk porosity and permeability measurements and finite element methods models, we show that the tabular fracture is at least two orders of magnitude more permeable than the host rock at mean stresses up to 90 MPa. Further, we show that the tabular fracture zone dilates as the stress state approaches the friction envelope resulting in up to a three order of magnitude increase in fracture permeability. These results indicate that the enhanced and stress-sensitive permeability in fault damage zones and sedimentary basins composed of arkosic sandstones will be controlled by the distribution of macroscopic fractures rather than microfractures.

show abstract

“…Various publications have studied injection-related fracturing mechanisms and characterized the Mode I, Mode II and mixed mode behavior caused by hydraulic injection (Nadimi 2015). Typical procedures for estimating the orientations of critically stressed fractures were presented by Ito and Hayashi (2003) and Nadimi et al (2016). Morris et al (1996) reaffirmed slippage tendencies, based on the ratio of the resolved shear stress to the resolved effective normal stress acting on a fracture plane.…”

Section: Introductionmentioning

confidence: 99%

Effect of natural fractures on determining closure pressure

Nadimi

Forbes

Moore

et al. 2019

J Petrol Explor Prod Technol

View full text Add to dashboard Cite

In Utah FORGE reservoir, eight pressure transient tests (microhydraulic fracturing and DFIT™) show natural fracture/ pressure-dependent leakoff. This behavior may lead to misinterpretation of the closure pressure (proxy for minimum principal stress). The closure pressures obtained from DFIT™ (or microhydraulic fracturing) testing may reflect shear failure along natural fractures or discontinuities rather than tensile failure and lead to inaccurate estimates of the minimum principal stress. In pressure tests conducted at the Utah FORGE site showed that reactivation or opening of natural fractures intersecting the wellbore and were suggested by multiple closure events in DFIT™ tests. In addition, comparisons between the pre-and postwell-tests FMI logs show that there are populations of induced fracture and reactivated natural fractures which are mostly vertical and sub-vertical. In this study, DFIT™ (or microhydraulic fracturing) test analysis and numerical simulations were used to suggest that hydraulic shearing of critically stressed natural fractures can contribute to multiple closure signatures and possibly lead to incorrect determination of the minimum principal stress. As other authors have previously advocated, the DFIT™ test analyses and numerical simulations suggest that better estimations of minimum principal stress may be derived by injecting at relatively high rate and pressure and insuring that tensile breakdown is reached. In addition, extended shut-in period is required to determine accurate reservoir characteristics and fluid flow regime. Keywords Utah FORGE • Microhydraulic fracturing and DFIT™ • Natural fracture/pressure-dependent leakoff • Minimum principal stress • Closure pressure • XSite™ 1 , 2 and 3 Maximum, intermediate and minimum principle stresses, respectively (psi) q Flow rate (bpm) P wf Well flowing bottomhole pressure (psi) P i Reservoir pore pressure (psi) II Injectivity index (bpm/psi)

show abstract

Role of Stress-controlled Flow Pathways in HDR Geothermal Reservoirs

Cited by 41 publications

References 13 publications

Stress-dependent permeability of fractured rock masses: a numerical study

Stress-dependent permeability of fractured rock masses: a numerical study

Stress‐dependent transport properties of fractured arkosic sandstone

Effect of natural fractures on determining closure pressure

Contact Info

Product

Resources

About